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A Pd-mediated intramolecular aryl-aryl coupling reaction of phenyl benzoate derivatives were examined to form benzo[c]chromen-6-ones, and then enantioselective lactone-opening reaction with a borane-oxazaborolidine combination was carried out. The resulting biphenyl was transformed into a key intermediate for the stegane related compounds. The absolute configuration of the biphenyl is also discussed. Stegane and related compounds are important because of their interesting biological activities such as antileukemic properties. 1 One of the most outstanding features of their chemical structures is an unsymmetrical 2,2'-disubstituted biphenyl moiety with an axial chirality (Figure 1). For the formation of such a biphenyl part in the syntheses of the stegane families, several approaches have been attempted such as photocyclization, 2 Suzuki coupling, 3 oxidative biaryl coupling, 4 the S N Ar reaction, 5 Ullmann coupling, 6

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Nitration of aromatic compounds is one of the most fundamental and useful reactions for introducing the nitrogen atom directly into aromatic rings. [1][2][3][4] This reaction generally requires the use of a potent mixture of concentrated or fuming nitric acid with sulfuric acid, a large amount of acid and its waste after the aqueous work-up procedures often cause serious environmental problems. In order to these issues, there have been some efforts to perform reactions in the absence of sulfric acid. For the solution of this problem, we focused on acyl nitrates, which are known as active nitrating agent. [27][28][29][30][31][32][33][34][35][36] Acyl nitrates are generally produced in situ by the reaction of an excess of concentrated or fuming nitric acid and carboxylic anhydride, or the reaction of silver nitrate and acid chloride. Another method for the generation of acyl nitrates is the reaction of inorganic nitrates and carboxylic anhydride, whereas, in most cases, the nitration by this method is limited to activated substrates. 37) Crivello reported that the acyl nitrates generated from the mixture of ammonium nitrate and trifluoroacetic anhydride and aromatic nitration smoothly proceeded, however, the reaction of ammonium nitrate with acetic anhydride did not produce nitration products. 38) It is known that rare earth metal(III) trifluoromethanesulfonates (rare earth metal(III) triflates, RE(OTf) 3 ) have a high Lewis acidity compared to the corresponding rare earth metal(III) halides, and are stable in water. In this decade, there have been many reports that RE(OTf) 3 as a Lewis acid catalyst has been successfully applied to several synthetic reactions.39-45) Recently, we have developed RE(OTf) 3 catalyzed Friedel-Crafts reactions [46][47][48][49] and benzyl-etherification, 50) and these reactions proceed smoothly using small amounts of RE(OTf) 3 . During the course of our investigations about Friedel-Crafts acylation, we found that acetyl perchlorate, the mixed anhydride of acetic acid and perchloric acid, which acts as an active acylating agent is generated from acetic anhydride and lithium perchlorate in the presence of RE(OTf) 3 . [46][47][48][49] Based on this consideration, the efficient generation of acyl nitrate is expected between an inorganic nitrate and carboxylic anhydride in the presence of RE(OTf) 3 , and we tried to examine the nitration of aromatic compounds using the RE(OTf) 3 -carboxylic anhydride-inorganic nitrate system. Results and DiscussionIn the first place, the catalytic activity of Lewis acids was examined for the nitration of m-xylene using the acetic anhydride-lithium nitrate system. These results are summarized in Table 1. The nitration of m-xylene was carried out in a solution containing 0.3 molar equivalent of Lewis acid, 5.0 molar equivalent of acetic anhydride, and 1.0 molar equivalent of lithium nitrate (LiNO 3 ) at room temperature. 1,3-Dimethyl-2-nitrobenzene (1) and 1,3-dimethyl-4-nitrobenzene (2) as nitration products were obtained. No di-nitrated products were observ...